검지offer: 지그재그 순서로 두 갈래 나무 인쇄

제목 분석

코드

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;
/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;
    }

}
*/
public class Solution {
    public ArrayList > Print(TreeNode pRoot) {
        ArrayList> res = new ArrayList<>();
        if(pRoot == null) {
            return res;
        }
        Queue q = new LinkedList<>();
        Stack s = new Stack<>();
        ArrayList layer = new ArrayList<>();
        q.add(pRoot);
        int start = 0;
        int end = 1;  //  
        boolean direction = false;  //  
        while(!q.isEmpty()) {
            TreeNode temp = q.remove();
            if(direction) {
                s.push(temp.val);
            } else {
                layer.add(temp.val);
            }
            start ++;
            if(temp.left != null) {
                q.add(temp.left);
            }
            if(temp.right != null) {
                q.add(temp.right);
            }
            if(start == end) {
                if(direction) {
                    while(!s.isEmpty()) {
                        layer.add(s.pop());
                    }                        
                }
                res.add(layer);
                start = 0;
                end = q.size();
                direction = !direction;
                layer = new ArrayList();
            }
        }
        return res;
    }

}